Tsubasa: Reservoir Chronicle. It's by CLAMP, the same group of writer/artists who made Cardcaptor Sakura, Chobits, Magic Knights Rayearth, Angelic Layer, and a few others. It's mainly about an alternate-universe pair of characters (originally from Cardcaptor Sakura) traveling through parallel worlds, in which pretty much every character they have ever drawn appears in alternate-universe form. Tsubasa overlaps chronologically with xxxHolic (also an anime by CLAMP) and has tie-ins to it, although xxxHolic is much darker and more stand-alone.
Sakura is the title character of Cardcaptor Sakura, and one of the main characters of Tsubasa: Reservoir Chronicle. She is the official Damsel In Distress.